Exhaust gas sensors are used in control systems for internal combustion engines in order to detect concentrations of various exhaust gas constituents and in order to implement a variety of control and regulation functions. In order to regulate the composition of an air/fuel mixture for the operation of internal combustion engines, the oxygen content of the exhaust gas is determined in their exhaust gas conduit by way of exhaust gas sensors (lambda probes). An unequivocal correlation between the variable to be measured, the lambda value, and the output signal of the lambda probe (the probe voltage) is necessary for correct operation of the lambda probe over the entire service life, taking into consideration aging effects and tolerances. In order to compensate for tolerances and aging effects it is known to perform a comparison, during coasting phases and while excess oxygen is present in that context in the exhaust gas conduit, of the probe characteristic curve with a reference characteristic curve, and to derive therefrom a correction of the output signal of the lambda probe. What can in fact be achieved with such a procedure is that constant regulation of the lambda value can be carried out by way of a two-point lambda probe upstream from the first catalytic converter in the exhaust section.
Suitable coasting phases are becoming increasingly rare in more recent vehicle concepts, however, for example hybrid drives made up of internal combustion engines and electric drives, or drivetrain gliding, so that correction in a context of an excess of air cannot occur, or at least cannot occur often enough.
A secondary air inlet, which enables optimum operation of a catalytic converter or particle filter mounted downstream from it in the exhaust gas conduit by the fact that its operating temperature is reached more quickly or regeneration is better enabled, is present in some cases in exhaust gas systems of internal combustion engines.
German Patent Application No. DE 10 2013 201 257 A1 describes a method in particular for off-highway applications in which coasting phases for carrying out calibration of the lambda probe are not, or not sufficiently, present, in which method upon shutoff of the internal combustion engine firstly its rotation speed is elevated and then fuel delivery is interrupted. In the run-on of the internal combustion engine that then occurs, air is drawn in by it and discharged into the exhaust gas conduit. In this phase a sufficiently high oxygen concentration for calibration of the lambda probe exists. German Patent Application No. DE 10 2013 201 257 A1 is therefore based on the same object as the present invention, but the excess air is generated in a completely different way.
German Patent Application No. DE 10 2013 201 316 A1 describes the generation of excess air in the region of an exhaust system by the fact that in a coasting mode of the internal combustion engine, the internal combustion engine is driven by an electric motor of the drive unit embodied as a hybrid drive. An excess air concentration is thereby generated in the exhaust gas conduit, and calibration of an exhaust gas probe disposed therein is enabled.
German Patent No. DE 197 34 670 C1 describes a method with which lambda probes connected in transposed fashion can be detected in internal combustion engines having multiple outlet ducts. For testing, air is delivered by way of an air source (secondary air pump) individually to at least one exhaust gas duct upstream from a respective lambda probe. Based on the change in the lambda signal which results therefrom, it is possible to check whether the lambda probes are correctly connected or have been transposed.
German Patent No. DE 195 36 577 C2 describes a method for checking the functionality of a heating device of a lambda probe. An operating state of the internal combustion engine in which a lean mixture is definitely present is selected for this purpose. The probe voltage is regulated by way of the heating device to a predetermined diagnostic target value. A fault in the heating device is detected if the diagnostic target value is not reached within a predetermined time. The operating state can be brought about by way of an injection of secondary air into the exhaust section.
An object of the present invention is to provide a method that enables correction of an output signal of an exhaust gas sensor with excess air in the exhaust gas, independently of an availability of coasting phases in the context of the operation of an internal combustion engine.
A further object of the present invention is to provide a control device suitable for carrying out the method.